I. Field of the Invention
This invention relates to a liquid crystal element with an improved orientation layer, which is used in display panels, liquid crystal shutters and the like.
II. Description of the Prior Art
A conventional liquid crystal element comprises a pair of glass substrates secured by a sealing material to face each other so as to define a chamber therebetween. An electrode film for conducting electric power for driving the element is attached on the outside of each of the substrates. On the inside of each substrate, an orientation layer for orienting liquid crystal contained in the chamber is formed. To obtain a high contrast ratio and quick response characteristics of the element, the liquid crystal should have a high degree of alignment. Thus, since the liquid crystal is oriented by the orientation layer, the performance of the orientation layer is very important for obtaining a high contrast ratio and quick response characteristics of the liquid crystal element.
Polymers such as polyimide, polyamideimide, polyphenylene oxide and polysulfone are conventionally used for forming the orientation layer of a liquid crystal element. Among these, in view of the heat resistance, adhesiveness, insulation ability and film-forming capacity, the most reliable and most widely used polymer is liquid polyimide (Japanese Patent Disclosure (Kokai) Nos. 56817/82 and 230635/87). However, liquid polyimide has an unsatisfactory performance in the capacity of orienting the liquid crystal molecules. In particular, in a ferroelectric liquid crystal display which is now being developed as a new generation liquid crystal display, the liquid crystal molecules must be oriented into chiral smectic C phase in which the liquid crystal molecules must be arranged almost as in a crystal. It is very difficult to align the liquid crystal molecules in a satisfactory degree with the polyimide. Thus, orientation layers for the high dielectric liquid crystal display are now being intensively investigated by modifying the polyimide (e.g., Japanese Patent Disclosure (Kokai) Nos. 87939/87 and 98327/87). Since polyimid is formed, however, by the reaction between an amine and a carboxylic acid derivative, free ionic groups due to the unreacted amine or carboxylic acid derivative may remain in the layer, which degrade the high degree of alignment of the liquid crystal molecules.